First off if the video in mind is somewhat objectionable or you wouldnt want your boss to watch it with you - then dont post it here. I will delete it.

Posting YouTube videos is very easy.

Step 1. Create a new thread or reply to an existing thread
Step 2. Locate your video on YouTube
Step 3. Copy the string of characters AFTER THE EQUALS SIGN, at the end of the web address in your browser - example below

Step 4. After you have typed your message drop down a line or tube and type the following:
Step 5. Paste the string of characters you copied in between the two middle brackets. Using the above example it should look like this